One day, long long ago, a little baby was born(出生). His name was Jesus(耶稣). Jesus was a special baby. Many people said he was the son of God(上帝). When he was born, a new star was in the sky. Three wise men saw the star. They followed the star to Jesus. They brought the baby special gifts. When the baby grew into a man, he was a great teacher. He taught people to love God and to love each other. Jesus's birthday，December 25th, is Christmas Day. We give gifts to our friends and family at Christmas. We put stars on our Christmas trees, too.

圆$x^2+y^2=4$截直线$\sqrt{3}x+y-2\sqrt{3}=0$所得弦长是（   ）